By 1993, both known cannabinoid receptors had been identified. Since then, a key question has hovered over the cannabinoid field: is that all there is or do additional cannabinoid receptors remain to be discovered? Indirect evidence supports as many as three additional 'cannabinoid' receptors in the hippocampus, but no receptors have been molecularly identified. If it were possible to clearly identify and isolate a neuron mediating a non-CB1 cannabinoid response, then it should be possible using existing technologies to identify and clone the receptor. The cloning of a novel cannabinoid receptor would be a major development in the cannabinoid field. In the process of studying endocannabinoid plasticity in cultured autaptic hippocampal neurons (DSE) I have identified five subpopulations of excitatory neurons, two of which exhibit distinct responses to cannabinoids, even in the absence of CB1 receptors. Because autaptic neurons are solitary it is possible to extract the entire cell mass nearly intact. Thus I am in a position to pharmacologically identify and isolate examples of two neuronal subpopulations each expressing a distinct non-CB1 cannabinoid receptor. The specific aims of the proposal are to: 1. Characterize the cannabinoid-like response in both neuronal subpopulations using electrophysiological methods. This constitutes the bulk of proposed experiments and is largely independent of (but would be greatly enhanced by) Specific Aim #2. 2. Identify the two novel cannabinoid receptors. This will be done by extracting and amplifying RNA from each subpopulation, and then cloning the receptor using gene array and candidate gene approaches. Discovery of two new cannabinoid receptors would have considerable health implications. Marijuana is a major drug of abuse, acting via cannabinoid receptors. Knowing the identity and function of all cannabinoid receptors is key to understanding how marijuana affects the body. [unreadable] [unreadable] [unreadable]